Azo dyes and their method of



Azo nvns AND THEIR METHOD OF PREPARATION Bela Gaspar, Beverly Hills, andPaul Daniel Dreyfuss, Van Nuys, Califl; said Dreyfuss assignor, bydirect and mesne assignments, to Bela Gaspar, Beverly Hills, Calif.

No Drawing. Original application November 5, 1948, Serial No. 58,619,now Patent No. 2,644,753, dated July 7, 1953. Divided and thisapplication June 3, 1953, Serial No. 361,443

8 Claims. (Cl. 260144) The present invention relates to new azo dyes, toa method for their preparation and to their uses in color photography.

Processes of color photography depending upon the decolorization of dyesin the presence of metallic silver are well known. A process of thistype in which azo dyes are employed in multilayer coatings to producecolored images by bleaching the dyes in the presence of siliver imagesis disclosed in a number of patents, e. g. U. S. Patent 2,020,775. Inthis process azo dyes are uniformly distributed in photographiccolloids, and these are coated on a transparent or opaque support. Thematerial is exposed and developed and is then subjected to the action ofa bath which destroys the dye locally in the presence of the metallicdeposit of the photographic image. This results in the production of adye image which is reversed with respect to the metal image.

This application is a division of U. S. application Serial No. 58,619,filed November 5, 1948, now,Patent No. 2,644,753.

In the co-pending patent application, Serial Number 537,967, filed May29, 1944, now Patent No. 2,470,769, there are described a number of azodyes which areuseful in the above mentioned process and which belong tothe class of high molecular weightdyes wherein Ar and Ar" stand foraliphatic, aromatic or heterocyclic radicals; B stands for aheteronuclear bond linking a plurality of dye units; n stands for aninteger greater than one, and a stands for an integer from one to four,and the product of a and n is greater than two.

The term heteronuclear bond means a linkage, an atom or a radical whichlinks a plurality of dye units (ArN=N)Ar, provided that it interrupts,the con jugation of the chain. The dye unit can be amonoazo dye (a=1), atrue disazo (a=2), trisazo 01:33) or, generally, polyazo (a 1) dye.Whereas in a true polyazo dye, the azo groups are linked together by aconjugated system and, therefore, influence the chemical and opticalqualities of each other, the dye units in the high molecular weightdyes, as herein defined, are linked to,- gether by heteronuclear bondsand, therefore, do not appreciably influence the chemical and opticalqualities of each other.

The above general formula is valid for thesimplest case of highmolecular weight dyes containing heteronuclear bonds, i. e. it is validfor the case of only bivalent heteronuclear bonds such as-- (whichdenotes a carbon to carbon linkage), O--, -CH or SO;,-. If, however, allor part of the heteronuclear bonds are at least trivalent, such as thecyanun'c nucleus, the pentaerythrityl residue, etc., the polymeric dyesare not straight chains as it would appear from the above formula, butform a two-or-three di- United States Patent 2,844,574 Patented July 22,1958 mensional net of dye units. Dyes of this type are calledcross-linked in the following:

One method of obtaining dyes, having a straight chain formed by dyeunits and heteronuclear bonds, and of analogous cross-linked polymericdyes consists of coupling polyfunctional diazo components withpolyfunctiona1 azo coupling components.

In our co-pending application entitled Acylated Derivatives ofAminosulfonic Acids and Method for Their Preparation, Serial No. 58,620,filed on an even date herewith, now Patent No. 2,698,342, we havedisclosed a number of polyfunctional azo coupling components. These newazo coupling components, if applied to the technique disclosed in PatentNo. 2,470,769, are converted into dyes which prove to be of particularvalue,

The components of our co-pending application entitled AcylatedDerivatives of Aminosulfonic Acids and Method for Their Preparationwhich serve as starting materials in the manufacture of the new dyes ofthis invention, adhere to the general formula B [NZ-R 1 30 cation)". 4:

where R stands for the residue of naphthalene; whereas m stands for oneor two; Z stands for hydrogen or a hydrocarbon such as ethyl or phenylradical; B(OH) stands for the x valent residue of a b-basic organic acidB(OH) wherein x is greater than one and b is at least equal to x, suchas COCO, A(CO) A(-S0 (CO),,, A(-SO and a residue of the cyanuric typewhere A stands for a b-valent radical; where b stands for an integergreater than one and where P+q= Among the many azo coupling componentsof this general structure, we prefer those where 11:2, where the groups-NZ- and OH shown in the above formula stand in position -1,8 of thenaphthalene residue R, and where Z stands for hydrogen. Of particularimportance are those in which B(OH) is an x-valent radical derived froma b-basic organic acid B(OH);, selected from the group consisting ofpolycarboxylic and polysulfonic acid radicals of hydrocarbons andoxahydrocarbons.

Suitable coupling components from which the dyes of this invention maybe obtained are e. g. the following: N,N'-oxalyl-bis-J-acid;N,N'-adipyl-bis-(N-ethyl-gammaacid); N,N-azelayl-bis-M-acid;N,N-sebacyl-bis-I-acid; N,N'-terephthaloyl-bis-H-acid;N,N-m-phenylenediacetylbis-X-acid; N,N-diglycolyl-bis-H-acid;N,N'-hydroquinone-O-O-diacetyl-bis-H-acid; carbonyl bis[(4-aminobenzoyl)-H-acid]; succinyl-bis [6 (paminophenylureido)-1-naphthol-3-sulfonic acid]; N,N-naphthalene-1.5-disulfo-K-acid; N,N'-benzidinesulfonedisulfo-S-acid;furfurane-2,5-dicarboxylyl-H-acid; N,N'-(benzoyl-m-sulfo)- bis-I-acid;2(p-sulfanilino)-4,6-di[l-hydroxy 3,6 disulfonaphthylamino- 8)]-s-triazine; N,N,N"-t1icarballylyltris-J-acid;S-triazine-2,4,6-tricarboxylyl-l-I-acid;adipylbis-(aminoterephthaloyl-bis-K-acid) The coupling compounds of theabove exemplified class are coupled with polydiazo compounds derivedfrom polyamino compounds such as:3,3-diamino-4,4-dimethoxydiphenylmethane; 1,1-di-(p-aminophenyl)cyclohexane; 4,4'-di(p-aminobenzoyl)-amino stilbene-2,2 disulfonic acid;hydroquinone-di-(3-amino 4 propyloxybenzyl)ether;4,4-diaminodiphenylether; 4,4'-diaminodiphenlysu1fone-X,X-disulfonicacid; sebacyl-bis-(3 amino 4- 2,4,6-tri-(p-amino-m-sulfanilino-s-triazine) and the tetrazo compounds of U. S,Patent No. 2,263,994.

Among the polymeric azo dyes produced by coupling these polydiazocompounds with the above exemplified polyfunctionalacylarninonaphtholsulfonic acids many red, magneta, violet, blue andcyan dyes are found which satisfy the highest requirements formultilayer photographic materials.

The components are easily available. The dyes, having a sufficientlyhigh molecular weight, do not diffuse within photographic colloids; theyhave high tinctorial power, and many dyes of this class are easilysoluble, fast to light, very brilliant and are easily bleached at theplaces where metallic silver is present. They are reduced in thisbleaching process to form low molecular weight compounds which areeasily removed from the photographic colloid by washing.

Polymeric dyes, containing polyfunctional acylamino naphthol sulfonicacids as coupling components can be obtained by the above indicatedmethod (i. e. by coupling the polyfunctional acylaminonaphtholsulfonicacids with polydiazo compounds) or by other methods, as will be seenfrom the examples below.

These polymeric azo dyes may have at least one, preferably a plurality,of radicals each having the formula the values for R, Z, m and B beingthe same as those noted immediately above for these letters.

In a preferred embodiment, the polymeric azo dyes of the invention haveat least one, preferably a plurality, of radicals each having theformula nmgij 93mg (SO; ration) (SOs cation).

where B and m have the values noted above.

According to a most preferred embodiment, the polymeric azo dyes have atleast one, preferably a plurality, of radicals each having the formula(S O 3 cation) (S 3 cation) 90 where Y is a bivalent organic, e. g.aromatic, radical, and m has the values indicated above.

If the dyes are prepared by coupling polyvalent diazo compounds withpolyfunctional acylaminonaphtholsulfom'c acids, they will consist of alarge but undetermined number of dye units. In some cases it isexperimentally impossible to couple all available diazo functions withall available coupling positions. However, even in the case of completecoupling, a mixture of polymer homologous" dyes is formed, i. e. amixture of dyes which differ from each other by the number of dye unitswhich are present in each individual dye molecule. All dyes representedin this mixture have the same shade but they are different in otherrespects. For example, they are adsorbed with different ease tovegetable fiber or to activated aluminum oxide, or they precipitate withdifferent case from aqueous solution by the addition of electrolytes. Itis therefore possible to separate the larger dye molecules from thesmaller ones by fractional precipitation, by fractional adsorption, bydialysis through suitable membranes and by other means peculiar to eachcase. It has also been found that mixtures of polymeric dyes containinga large but undetermined number of dye units obtained from other lowmolecular components, such as, compounds having both diazo and couplingfunctions and mixtures comprising low molecular weight azo dyes havingreactive groups and polyfunctional compounds which are capable oflinking a plurality of said relative groups, may also be fractionatedadvantageously in order to obtain improved dye products.

The average number of dye units in a polymer homologous mixture can beinfluenced by varying the pro portion of the components; e. g., thepolydiazo compounds can be coupled with polyvalent acylaminonaphthol'sulfonic acids so that essentially each diazo group and essentially eachnaphthol residue take part in the re action (coupling 1:1), or one ofthe components may be present'in excess. If one of the components is inexcess, the average molecular weight of the polymeric dye decreases, andthe dye will contain terminal groups such as free coupling positions ordiazo groups or derivatives of conversion from the diazo groups whichhave marked influence on the physical properties of the dye. E. g.,' thebehaviour of the dye in the fractionation, the viscosity of its aqueoussolution, its aflinity to substrata, and its diffusion in photographiccolloids vary according to the proportion of the components used in thecoupling of the dye.

The character of the terminal groups has furthermore some influence onthe substantivity of the dye with respect to gelatin. Both thesubstantivity and the molecular size of the dye contribute to itsfastness with regard to diffusion. As a small molecule obviouslycomprises more terminal groups than a large molecule does, we found itadvantageous in some cases to sacrifice molecular size in favor ofterminal groups. That is, the optimum results with regard to diffusionare not necessarily obtained with dyes which are prepared from polydiazocompounds and polyvalent coupling components in a ratio 1:1 but othercoupling proportions such as 2:1 or 1:2 may be preferable. Sometimeswide variations are possible, particularly-when the components containthree or more functional groups. For example, to mention an extremecase, N=(3'-amino-4methoxy-benzyl)-anhydroaminobenzylalcohol' can becompletely diazotized and coupled in proportions varying between 4:1 and1:4- with the product'obtained from an ethylene-maleic anhydrideinterpolymer and H-acid '(our co-pending application entitled AcylatedDerivatives of Aminosulfonic Acids and Methods for Their Preparation).All the magenta dyes obtained from these two components do not diffuse,and all of them are easily water soluble.

Like the dyes obtained by coupling polydiazo with polyvalent couplingcompounds, other dyes obtained by' polyconden'sation must notnecessarily be produced with the highest molecular weight possible. Forexample, a compound comprising one diazotizable amino group and onecoupling function'such as the intermediate of Example 2 below, ifdiazotized and coupled with itself, is converted into a polymerhomologous dye mixture, particularly when the diazotization and/ or thecoupling are incomplete. This mixture of dyes can be separated intofractionsv which are optically identical but are different in other"respects.

Polymer homologous dye mixtures obtained by condensing simple dyeshaving a plurality of reactive terminal groups, such as amino groups,with polyvalent reagents, such as halides of polyacids, can be likewiseimproved by fractionation.

If a polyfunc'tional diazo component is coupled with a polyfunctionalcoupling component in a proportion other than 1:1, the coupling productcan be modified by subsequent addition of a component able to react withthe terminal groups of said coupling product; e. g., a dye obtained bycoupling a polydiazo compound with an excess of a polyfunctionalcoupling component, can be modified by after-treatment with a monodiazocompound.

It must be determined empirically in each case, in what proportion thediazo and the coupling components are to be combined in order to producea non-diffusing polymeric dye. Generally, an excess of diazo compound upto 100% has a beneficial effect on the fastness of the dye with regardto diffusion; however, in some cases an excess of coupling compound upto 100% acts in the same way. In other cases the optimum results areobtained by coupling 1:1. A 2 to 3 percent variation in the proportionsgenerally causes noticeable differences in the physical properties ofthe dye obtained. In certain cases a dye, obtained by coupling 1:1, ifdissolved and added to the emulsion, increases the viscosity of theemulsion and makes it difficult to obtain an even coating. A deviationof a few percent from the proportion 1:1 will lower the viscosity of thedye solution without appreciably changing the fastness of the dye withregard to diffusion.

Example 1 1.3 mols of 4,4'-diaminodiphenylether is tetrazotized andcoupled in aqueous pyridine with 1.0 mol of N,N'-

described in our co-p ending application entitled Acylated Derivativesof Aminosulfonic Acids and Method for Their Preparation, now Patent No.2,698,342. According to said co-pending application, the above adipylbis-H acid is prepared by reacting1-amino-8-hydroxy-naphthalene-3,6-disulfonic acid (H-acid) with atertiary nitrogen base such as dodecyldimethylamine to form a salt, andacylating the resulting salt with adipyl chloride in the presence of anorganic solvent such as pyridine and under essentially anhydrousconditions. product is then reacted with sodium acetate to split off thedodecyldim ethylamine and form the sodium salt of N,N'-adipyl-bis-H acidas product. A brilliant magenta dye forms Which, if tested inphotographic gelatin, shows traces of diffusion. The dye is isolated andtreated in weakly acidic solution with such an amount of alumina as toadsorb of the total dye weight. The dye in solution (85%) is completelyfreed from aluminum ions and isolated as the sodium salt. The absorbeddye (15%) is eluted with sodium carbonate and isolated in the samemanner. While the fraction which had been adsorbed diffuses about tentimes as much as does the raw dye, the other 85% of the dye iscompletely fast to diffusion, even after prolonged treatment in alkalineprocessing baths. The diffusing and the non-diffusing fractions have thesame absorption spectrum; both are very water soluble, cause nodesensitization of the emulsion and are quite stable to light.

If the components of the above example are coupled in a ratio 1.521, araw dye is obtained which diffuses less than the raw dye obtained in thecoupling 1.3:1. This The acylated Example 2 One mol ofp:phenylenediaminesulfonic acid is stirred in aqueous solution at 0 C.in the presence of an excess of sodium acetate with the dichloride of2-furoic acid-5- sulfonic acid (1 mol). After 1 hour H-acid (1 mol) isadded and the temperature slowly raised. The product which can beisolated from the reaction mixture by addition of potassium carbonate isbelieved to have the following structure:

KOsS- $0 K If this compound is treated with nitrous acid at pH-S or withnitrous acid at low pH (about 2) and thereupon the pH is raised to 8, abrilliant magneta dye forms, which, even without fractionation, diffusesonly very little in gelatin.

Example 3 The intermediateof the foregoing example can serve in thesynthesis of a polymeric dye having a determined number of azo units. E.g., 3,3'-diamino-4,4-dimethoxydiphenylmethane (1 mol) is tetrazotizedand coupled with 2 mols of the above intermediate. If the resultingproduct is tetrazotized and coupled with a terminal coupling componentsuch as (2,4-dichlorobenzoyl)-K-acid, a nondiifusing magenta tetrakisazodye is obtained.

Other'colors can be produced by coupling the tetrazotized diaminodiazodye of this example with different terminal coupling components; e. g.,non-diffusing red dyes are produced by coupling it with succinyl-bis-(paminophenyl)-pyrazoloue-carbonic acid or with glycerina,a-bis-acetoacetate.

, Example 4 One mol of 4-chloro-2-aminoanisole is diazotized and coupledwith 1 mol of N,N'-(aminohydroquinone-O-O- diacetyl)-bis-H-acid(obtained by reduction of the corresponding nitro compound). The dyewhich forms is supposed to be essentially a monoazo dye. This dye is"diazotized and coupled with itself whereby a nondiffusing polymeric azodye of undetermined molecular Weight is formed.

If in the first operation 2 mols of chloranisidine were used, anaminodisazo dye forms which by diazotization and coupling it with2,4-dichlorobenzoyl-K-acid is converted into a. non-difiusing magentatrisazo dye.

I 7 Example 5 2-naphthylamine-4,8-disulfonic acid is diazotized andcoupled with l-naphthylamine-7-sulfonic acid. A monoazo dye forms whichis diazotized and coupled with 2- ethoxy-1-naphthylaminc-7-sulfonicacid. The disazo dye which forms is a well known intermediate. It iscustomary in the manufacture of trisazo dyes to diazotize thisintermediate and couple it With a terminal component with out particularprecautions. However, in order to prepare the polyazo dye of thisexample, it is necessary to isolate said intermediate in a pure state.It is repeatedly dissolved and reprecipitated by addition of salt untilall impurities are removed. This purification is performed in avoided.

Two molecular parts of the disazo dye are diazotized and "coupled at -15C. in 70% aqueous .pyridine with one molecular part of -'N,N'-adipylbis-(z-amino-d naphthol-7-sulfonic acid). A cyan .dye forms which ispurified by reprecipitation' from water and finally by precipitationwith acetone from the aqueous solution. The dye does not diffuse and hasexcellent photographic properties.

Example 6 An emulsion, sensitized to red light and containing a cyan dyeis coated on an opaque support as described in Example 4 of ourco-pending application, S. N. 18,714, filed April 2, 1948, now PatentNo. 2,612,448. A silver halide gelatin emulsion sensitized to greenlight and containing the non-diffusing fraction of the magenta dye ofexample 1 (0.5 gr./ 100 ml. emulsion) is coated thereon. A yellow filterlayer and a blue sensitive silver halide emulsion layer containing ayellow azo dye are coated on top, to complete a color photographicprinting material. This material is'exposed to light through a coloredtransparency, developed, bleached in a bleaching bath such as describedin U. S. Patent Re. 22,308, washed to remove the reduction products fromthe material, and liberated from silver and silver salts in knownmanner. A print in natural colors results.

Example 7 Anacid suspension of one mol of tetrazotized benzidine2,2'-disulfonic acid is poured into an acid solution of 2.2 mols ofo-anisidine, the solution is buttered with sodium acetate until onlyweakly acidic to Congo paper, the solution is stirred for 24 hours toallow for complete coupling, heated to 80 C. and cooled. The dye isfiltered, 'slurried in diluted hydrochloric acid, filtered, washed withalcohol and dried.

400 grams of the dry dye are stirred into 1.6 liters of fuming sulfuricacid (30% S0 at a temperature. below 10 C. The sulfonation mixture iskept at room temperature for three days and stirred slowly into crushedice. The sulfonated dye is precipitated with sodium chloride, filteredand purified by reprecipitation with sodium .chloride from aqueoussolution.

A tetrazo solution, prepared from 1.1 mol of the sultonated'dye, isadded to a pyridine solution of 1.0 mol of adipyl-bis-H-acid at 0 C.After two hours the solution is heated to 70 C., cooled to roomtemperature and acidi fled by addition of hydrochloric acid. The dye isprecipitated by addition of salt, filtered, washed with salt solution,dissolved in water, precipitated with sodium acetate, filtered andwashed with alcohol.

The magenta dye, thus obtained, is believed to have essentially thefollowing structure:

0 CH3 OH NH-CO-CHrOHz- SO Na SOaNa NaOiS This magenta dye is well watersoluble, stable to light, and a photographic layer dyed with this dye,bleaches well at the places where metallic silver is present. ,For mostpurposes, the dye can be regarded asnon-difiusing. How: ever, it is seenfrom rigid tests, i. e. at a high dye/ gelatin ratio, that the diffusionis still noticeable.

If this dye is dissolved in a sodium carbonate solution and precipitatedwith a quantity of sodium chloride which is insufiicient for completeprecipitation, a fraction is obtained which has the same characteristicsas has the raw dye except that it diffuses less. E. g., a recovery inone reprecipitation yields a dye which difius'es less than half of whatthe original dye difiuses. A repeated reprecipitation yields a stillless diffusing dye.

The dyes of this invention are suitable for use in emulsion and in lightscreening layers, in overcoats and interlayers, in photographic film,plates or paper. They can be used to dye the photographic colloiditself, or to dye up resins which afterwards may bedispersed inphotographic colloids. They can be mixed with unsensitized emulsions orwith emulsions which are sensitized to any color. They may beincorporated in any or all desired layers of a multilayer coating. Thesensitive compositions containingthese dyes may be coated on transparentor opaque supports, in single-layer or multi-layer coatings, or inmulti-layer coatings .on one or both sides of a support. The dyes ofthis invention, incorporated into one or more layers of photographicmaterial, may be bleached locally at the places where metallic silver ispresent by treatment in an acid, neutral or alkaline bleaching bath; orthey may be bleached or converted into other colored substances locallyat the places where developable silver salts are present, by treatmentin suitable developers.

The properties of the dyes of this invention, particularly their reducedtendency to penetrate colloids, make them valuable not only forphotographic purposes, but as well in other fields, e. g., in the dyeingof textiles and of artificial resins.

Since from the foregoing description of the invention it will beapparent to those skilled in the art that many variations .of thisinvention may be made without departing from the spirit and scopethereof, it is to be understood that we do not limit ourselves to thespecific examples thereof, except as defined in the appended claims.

We claim:

1. A polymeric azo dye which is non-difiusing in photographic gelatincomprising a plurality of radicals each having the formula wherein Bstands for an x valent radical of a b-basic organic acid B(OH) x standsfor an integer of 10m 2 to 3, b is an integer at least equal to x andnot greater than 3, Z stands for a radical selected from the groupconsisting of hydrogen, ethyl and phenyl radicals, R is a naphthalenenucleus, m is an integer of from oneto two, Y stands for a bivalentaromatic radical, and where the azo groups shown in the formula arepart, of a total of n azo groups, said 21' groups being arranged in aplurality of dye units each containing an aromatic nucleus connected toan azo group, said dye units being separated from each other byheteronuclear bonds which interrupt the conjugation of the polymericchain, each .unit comprising I a--; azo groups where a stands for aninteger of from one to four, where n'=a.n is greater than 17, and wheren is the total number of said dye units. 7

2. A polymeric azo dye which is non-diffusing in photographic gelatincomprising a plurality of radicals each having the formula wherein Bstands for the b valent radical of a b-basic organic acid B(OH) b is aninteger of from Z to 3, Z stands for a radical selected from the groupconsisting of hydrogen, ethyl and phenyl radicals, R is a naphthalenenucleus, m is an integer of from one to two, and where the azo groupsshown in the formula are part of a total of n azo groups, said n groupsbeing arranged in a plurality of dye units each containing an aromaticnucleus connected to an azo group, said'dye units being separated fromeach other by heteronuclear bonds which interrupt the conjugation of thepolymeric chain, each unit comprising azo groups where a stands for aninteger of from one to four, where n=a.n is greater than b, and where nis the total number of said dye units.

3. A polymeric azo dye which is non-diffusing in photographic gelatin,comprising a plurality of radicals each having the formula N=N N=N HORZNBNZR:OH

(cation 038). (S03 Cation). where R is a naphthalene nucleus, Z is aradical selected from the group consisting of hydrogen, ethyl and phenylradicals, m is an integer of from one to two, and B is a b-valentdicarboxylic aliphatic acid acyl group, where b is 2, and where the azogroups shown in the formula are part of a total of n azo groups, said ngroups being arranged in a plurality of dye units each containing anaromatic nucleus connected to an azo group, said dye units beingseparated from each other by heteronuclear bonds which interrupt theconjugation of the polymeric chain, each unit comprising azo groupswhere a stands for an integer of from one to four, where where Y is abivalent aromatic radical and m is an integer of from one to two, andwhere the azo groups shown in the formula are part of a total of n azogroups, said n groups being arranged in a plurality of dye units eachwhere a stands for an integer of from one to four, where n=a.n isgreater than 2, and where n is the total number of said dye units.

6. A polymeric azo dye which is non-diffusing in photographic gelatin,formed by coupling a polydiazo compound with a coupling component of theformula HO OH /RZNBNZR (cation 03S). (S0 cation)".

where R is a naphthalene nucleus, Z is a radical selected from the groupconsistingof hydrogen, ethyl and phenyl radicals, m is an integer offrom one to two, and B is a dicarboxylic aliphatic acid acyl group.

7. A polymeric azo dye which is non-diffusing in photographic gelatin,formed by coupling tetrazotized di- 0 aminodiphenyl ether withadipyl-bis-H-acid, said dye having a plurality of radicals each havingthe formula --N=N N==N N=N D G cation 0 8- S0; cation cation 053- 80acation nqn is greater than b, and where n is the total number of saiddye units.

4. A polymeric azo dye which is non-diffusing in photographic gelatin,comprising a plurality of radicals each having the formula haw mam wherea stands for an integer of from one to four, where n'=a.n is greaterthan b, and where n is the total number of said dye units.

5. A polymeric azo dye which is non-diffusing in photographic gelatin,comprising a plurality of radicals, each having the formula OHNH-CO-(CHDr-OO-NH OH a cation), O; cation) 8. A polymeric azo dye whichis non-difiusing in photographic gelatin, comprising a plurality ofradicals each having the formula anti) where B stands for a b-valentdibasic organic acyl group, where b is 2, m is an integer of from one totwo, and where the azo groups shown in the formula are part of a totalof n azo groups, said n groups being arranged in a plurality of dyeunits each containing an aromatic nucleus connected to an azo group,said dye units being separated from each other by heteronuclear bondswhich interrupt the conjugation of the polymeric chain, each unitcomprising n azo groups where a stands for an integer of from one tofour, where n'=a.n is greater than b, and where n is the total number ofsaid dye units.

References Cited in the file of this patent UNITED STATES PATENTS2,104,595 Schirm Jan. 4, 1938 2,164,785 Rossander July 4, 1939 2,263,994Knight Nov. 25, 1941 2,644,753 Gaspar et al. July 7, 1953 FOREIGNPATENTS 819,778 France July 19, 1937

1. A POLYMERIC AZO DYE WHICH IS NON-DIFFUSING IN PHOTOGRAPHIC GELATINCOMPRISING A PLURALITY OF RADICALS EACH HAVING THE FORMULA